1. Technology Field
The present invention generally relates to semiconductor optical devices. In particular, the present invention relates to a method for applying coatings to facets of a laser device so as to protect the facets from damage during the coating process.
2. The Related Technology
Semiconductor lasers are currently used in a variety of technologies and applications, including communications networks. One type of semiconductor laser is the distributed feedback (“DFB”) laser. The DFB laser produces a stream of coherent, monochromatic light by stimulating photon emission from a solid state material. DFB lasers are commonly used in optical transmitters, which are responsible for modulating electrical signals into optical signals for transmission via an optical communication network.
Generally, a DFB laser includes a positively or negatively doped bottom layer or substrate, and a top layer that is oppositely doped with respect to the bottom layer. An active region, bounded by confinement regions, is included at the junction of the two layers. These structures together form the laser body. A grating is included in either the top or bottom layer to assist in producing a coherent light beam in the active region. The coherent stream of light that is produced in the active region can be emitted through either longitudinal end, or facet, of the laser body. DFB lasers are typically known as single mode devices as they produce light signals at one of several distinct wavelengths, such as 1,310 nm or 1,550 nm. Such light signals are appropriate for use in transmitting information over great distances via an optical communications network.
The two facets of the DFB laser described above are typically coated with a coating material that optimizes the emission of light from the active region. During a typical coating process, the laser is placed in a coating chamber, which is then evacuated. A full coating is then applied to a first facet of the laser before the vacuum in the chamber is released, the laser is rotated 180 degrees, and a full coating applied to the second facet.
One challenge with known coating processes such as the one described above relates to the second facet, which remains uncoated and unprotected during the full coating phase of the first facet. Due to the plasma environment found in the coating chamber during the coating process, damage may occur to the second facet while the first facet coating process is carried out, a process that can last from two to ten hours or more. Damage to the second facet in this manner can result in a substantial reduction in yield during laser manufacture.
Damage to the second facet similar to that just described can also occur in other coating processes, such as e-beam evaporation procedures, which are typically executed at elevated temperatures. Commonly performed at a deposition temperature of 150-200 degrees Celsius, the e-beam evaporation process is typically such that the second facet of the laser remains exposed for a prolonged period of time, undesirably allowing damage thereto to occur.
In light of the above discussion, therefore, a need exists in the art for a method by which facets of a laser, such as a DFB laser, can be spared from damage during the facet coating process, thereby increasing laser yield and improving overall laser performance.